In order to more fully exploit the available ground area for growing plants, e.g., in greenhouses, gardens, and the like, it has been proposed to grow the plants at a plurality of different levels. One technique developed for this purpose includes a vertical pipe filled with a plant growing medium and having walls pierced at various levels for accommodating the stems of the plants. Thus, the plant roots are located within the pipe and are nourished by the plant growing medium, water and fertilizer within the pipe, whereas the plant stems and fruit carried by the stems grow externally of the pipe. However, this technique was found unsatisfactory because of the lack of sufficient horizontal soil area, and also because of excessive soil compression at the lower levels.
Another system, described in U.S. Pat. No. 5,136,807, includes a plurality of containers stacked one on top of the other, with each container supporting the overlying containers but allowing open spaces between the side walls of the containers for growing the plants. Such an arrangement, however, also limits the amount of horizontal soil area available for plant growth and is subjected to excessive compression because of the weight of the overlying containers.